The present invention relates to a car-carried indicating device of the type in which light transmitted through a transparent portion of a needle plate, rotated by a meter internal unit, is used as a needle.
An analog meter of a self-illumination type has been known as a car-carried indicating device for transferring drive information, such as running speed, to a driver. In this type of the analog meter, a linear transparent part is formed in a disc-like needle plate, which is rotated by an internal unit for meter. A linear form of light transmitted through the transparent part is used as a needle.
Referring to FIGS. 43 to 46, there are shown conventional car-carried indicating devices of this type. A character plate 1 as a light diffusion plate is mounted on a meter case installed in a dash board of a motor vehicle. The character plate 1 contains a transparent portion 2, substantially circular in shape, at the location for display. A series of numerals 3a is circularly arrayed around the transparent portion 2, and further a scale 3b is circularly arrayed outside the series of numerals. An opaque layer 4 of black, for example is layered on the upper surface of the character plate 1, except the transparent portion 2, the numerals 3a and the scale 3b. A center hole 5 is formed at the center of the transparent portion 2. A rotating shaft 7 of the internal unit of the cross coil type, which is driven in accordance with given measuring quantities, passes through the center hole 5.
A disc-like needle plate 8 is disposed on the front side of the character plate 1. The needle plate 8 is made of transparent material, such as acryl and polycarbonate. The diameter of the needle plate 8 is slightly larger than that of the transparent portion 2. The rotating shaft 7 is connected to the needle plate 8. A transparent slit 9 is formed in the needle plate 8. The slit 9 serves as a needle extending radially from the center. The opaque layer 4 is also formed on the upper surface of the needle plate 8 except the slit 9. On the rear side of the character plate 1, a cold cathode tube 10 as a light source is disposed around the internal unit 6. The cold cathode tube 10 is shaped circular.
In the car-carried indicating device thus constructed, the cold cathode tube 10, when lit on, illuminates the rear side of the character plate 1. Light passes through the transparent portion 2 to illuminate the rear side of the needle plate 8. With the back-light, the numerals 3a, the scale 3b, and the slit 9 emit light. Under this condition, the internal unit 6 is driven in accordance with determinate measuring quantities, so that the needle plate 8 is turned and the slit 9 points to corresponding positions on the numerals 3a and scale 3b. In this way, the analog indication is performed.
As shown in FIG. 46, the needle plate 8 is slightly larger than the transparent portion 2 of the character plate 1. The circumferential edge part 8a of the-needle plate 8 overlaps with the circumferential edge part 2a of the transparent portion 2. Otherwise, when a driver turns his eyes off the front position, he will see the transparent portion 2 through a gap a between the character plate 1 and the needle plate 8.
Where the character plate 1 and the needle plate 8 overlap, the distal end part 9a of the slit 9, because of presence of the overlapping part b, emits an insufficient quantity of light; otherwise it should emit light by the back-light. As a result, it loses its clear presentation. To cope with this, the opaque layer 4 is formed on the upper surface of the distal end part 9a.
Formation of the opaque layer 4 on the distal end part 9a reduces the length of the slit 9 emitting light. In other words, as shown in FIG. 44, it increases the space between the tip 9a' of the slit 9 and the numerals 3a. As a result, the driver cannot clearly perceive the needle and its indication. Thus, the readability of the indicating device is deteriorated.
With reduction of the slit length, the driver will mistakenly perceive the indicating device smaller than the actual one. This leads to impairment of the value of commodity.